The ability to deliver compositions to targeted environments and/or to selectively activate compositions within specific spatial regions is important in a variety of fields. For example, targeted drug delivery strategies can be employed to deliver pharmaceutical compositions to a subject in a manner that increases the concentration of the pharmaceutical composition in some parts of the body relative to others, which can allow one to prolong drug interaction with specific diseased tissues. The ability to deliver pharmaceutical compositions to specific tissues can reduce dosage frequency, reduce unwanted side-effects caused by interactions of the pharmaceutical with non-targeted tissues, and reduce the fluctuation in the amount of the pharmaceutical composition circulating in the blood stream. Similar strategies can be employed in imaging applications, where it might be desirable to produce images of certain targeted locations.
Many targeted activation and/or release mechanisms are triggered using ultraviolet or higher-frequency electromagnetic radiation. Often, such electromagnetic radiation is transported through tissue to trigger activation and/or release. High-frequency electromagnetic radiation can cause unwanted side-effects, including tissue damage. For example, high-frequency electromagnetic radiation can cause photothermal damage, in which tissues are heated by absorbed electromagnetic radiation, which can in turn cause denaturation of proteins, loss of molecular tertiary structure, and fluidization of membranes. Electromagnetic radiation can also cause photochemical injury, for example, by generating free radicals. High-energy electromagnetic radiation can cause photomechanical damage, applying compressive or tensile forces to tissues.
Accordingly, it would be desirable to limit the extent to which high-frequency electromagnetic radiation interacts with the tissue of a subject in targeted release and/or activation systems.